The cause was heart and lung failure, said Linda Alonso Lebrón, her niece.

In the attack in the Capitol, Ms. Lebrón and the other assailants fired from a spectator’s gallery just above the House floor, raining as many as 30 bullets into a chaotic chamber and wounding five congressmen.

Ms. Lebrón was imprisoned for 25 years and widely condemned as a terrorist, although proponents of Puerto Rican independence hailed her and her associates as revolutionary heroes. She ascended into a leftist pantheon with figures like Che Guevara, becoming the subject of books and artwork.

Ms. Lebrón always said she remained proud of the shooting, which came two years after Puerto Rico, formerly a territory of the United States, had become a commonwealth. She dismissed that status as only more colonization and demanded complete independence. On the day of the shooting, she said she had fully expected to give up her life.

But in her latter decades she came to believe that civil disobedience, like that at Vieques, was not only more moral than violence but more effective.

“There is no need now to kill for freedom,” she said in 1998.

After her release from prison, Puerto Ricans of all political stripes would hail her on the street — she typically dressed in black — as a sort of national elder. They called her only Doña Lolita. No last name was necessary.

On the blustery, rainy day of the shooting 56 years ago, Ms. Lebrón was a stylishly dressed 34-year-old woman with the looks of the beauty queen she had been as a youth. She wore bright lipstick.

Photo

Members of the Capitol Police held three Puerto Rican nationalists, including Lolita Lebrón, taken into custody on March 1, 1954, after a shooting from a House gallery.Credit
Associated Press

Firecrackers suddenly seemed to be exploding in the House chamber at 2:32 p.m., interrupting a debate about Mexican farm workers among the 243 representatives present. Congressmen dived and fell, though none were killed.

Piercing the confusion was the voice of Ms. Lebrón: “Viva Puerto Rico!” She emptied the chambers of a big Luger pistol, holding it in two hands and waving it wildly. She then threw down the pistol and whipped out a Puerto Rican flag, which she waved but never managed to unfurl fully. As she shouted, her companions trained their weapons on the House floor.

After she was arrested, the police found a note in her purse. “My life I give for the freedom of my country,” it read.

Ms. Lebrón was convicted of five counts of assault with a dangerous weapon and sentenced to serve from 16 years and 8 months to 50 years in prison. Her colleagues, Rafael Cancel Miranda, Andres Figueroa Cordero and Irving Flores Rodriguez, were convicted on more serious counts and each sentenced to 25 to 75 years in prison.

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All four shooters were later sentenced to an additional six years in another trial for seditious conspiracy.

Dolores Lebrón de Perez was born on Nov. 19, 1919, in Lares, P.R., a small town where her father was a coffee plantation foreman. She finished eighth grade, and she was elected “Queen of the Flowers of May” in a beauty pageant.

She had a daughter and a son, both of whom died years ago. Ms. Lebrón is survived by her husband, Dr. Sergio Irizarry; her sister, Aurea Lebrón; and two grandchildren.

In the 1940s, she moved to New York seeking a better life and found work as a seamstress. She became a follower of Pedro Albizu Campos, a nationalist leader. Deciding a drastic event was needed to highlight his cause, he assigned Ms. Lebrón to lead it, making her responsible for every detail.

“I had all the secrets, all the plans,” she said in an interview with The Washington Post Magazine in 2004. “Me and me alone.”

The planning was not perfect. The conspirators got lost on the way to the Capitol from Union Station and had to ask a pedestrian for directions.

At the trial, Ms. Lebrón sharply repudiated an argument by her own lawyer that the conspirators were mentally unsound, shouting “No! No! No!”

When the prosecution let a Puerto Rican flag drag on the floor, she whispered to her lawyer and he successfully objected.

In prison, she built an altar in her cell and said she had repeated ecstatic religious visions. She refused to apply for parole because that meant apologizing.

In 1979, President Jimmy Carter, saying he was acting out of “humane considerations,” released Ms. Lebrón and two other assailants, a move that was expected to clear the way for the release of four Americans being held in Cuban prisons. He had released the fourth assailant in 1978 because he had cancer.

Many Puerto Ricans opposed the clemency. Puerto Rico’s nonvoting representative in Congress at the time, Baltasar Corrado del Río, said the assailants had been “kept in jail for their criminal conduct, not their political beliefs.”

Ms. Lebrón herself remained defiant after her release, saying it “was done for political expediency and not because of a concern for human rights.”

Correction: August 7, 2010

Because of an editing error, an obituary on Tuesday about Lolita Lebrón, the Puerto Rican nationalist who led an attack on the United States House of Representatives in 1954, misstated the name of the Puerto Rican representative in Congress who criticized President Jimmy Carter’s decision to release her from prison in 1979. He is Baltasar Corrada del Río, not Baltasar Corrado.

A version of this article appears in print on August 3, 2010, on Page A17 of the New York edition with the headline: Lolita Lebrón, Puerto Rican Nationalist, Dies at 90. Order Reprints|Today's Paper|Subscribe